The present invention relates generally to transfer cases for use in four-wheel drive vehicles. More particularly, the present invention relates to a system to provide a clutch pack slip control mode and range selector shift function to a transfer case clutch and range selector.
The drivetrain in many light-duty and sport-utility vehicles includes a transfer case for transmitting drive torque for the engine and transmission to all four of the wheels, thereby establishing a four-wheel-drive mode of operation. To accommodate differing road surfaces and conditions, many transfer cases are equipped with a gear reduction unit that can be selectively shifted by the vehicle operator to establish four-wheel high range and low range drive modes.
In addition, current control of transfer case clutch packs allows high slip conditions to occur. After a short period, approximately 10 seconds, the motor actuator locks up the clutch pack using a brake to prevent the motor and clutch pack from overheating. At full lock, speed differential on the clutch pack is zero, thereby generating no heat. This mode of operation is not always appropriate in certain situations.
It would be desirable to provide an electrohydraulic actuator system for a drivetrain transfer case that overcomes these and other disadvantages
The object of this invention is directed to an improved control system and actuator for a transfer case. More particularly, this invention is directed to an electrohydraulic actuator and control system for a transfer case.
One aspect of the present invention provides an electrohydraulic control system for a vehicle drivetrain transfer case that includes an actuator for generating fluid pressure. The system also includes an isolation valve and a control valve in fluid communication with the actuator and a clutch pack. The isolation valve is in a normally closed position and the control valve is in a normally open position. The system further includes a piston for applying fluid pressure to the clutch pack of the transfer case.
Another aspect of the invention provides a hydraulic control system for a vehicle drivetrain transfer case that includes an actuator for generating fluid pressure. The system also includes a first piston for applying fluid pressure to a first device, a selector piston for applying fluid pressure to a second device, and a shuttle valve positioned between the actuator and the second piston. The shuttle valve is in fluid communication with the actuator via a first and a second selector fluid line and in fluid communication with the second piston via a second and a third fluid line.
The invention further provides a method of generating hydraulic pressure for a vehicle drivetrain transfer case that includes generating fluid pressure, applying the fluid pressure to at least one piston, and controlling the fluid pressure to the at least one piston.
Yet another aspect of the invention provides a system for a vehicle drivetrain transfer case comprising means for generating fluid pressure, means for isolating an at least one device from the pressurized fluid, means for applying fluid pressure to the at least one device, means for controlling the pressurized fluid, and means for sensing fluid pressure.